Bolted-up friction joints in structural steel-work

ABSTRACT

The mating faying surfaces in a structural steel-work joint are protected by a layer of corrosion-resisting material such as primer or galvanizing. This layer carries a further layer of a friction agent comprising a binder and friction-increasing particles such as grit or amorphous aluminum particles. Both layers can be works-applied for greater reliability and consistency. The joint can be dismantled and reassembled without difficulty. The layer of corrosive-resisting material will be applied as an all-over protective layer for complete steel works components after cleaning off mill-scale.

United States Patent Brown et a1.

[451 Sept. 19, 1972 [54] BOLTED-UP FRICTION JOINTS IN STRUCTURALSTEEL-WORK Inventors: Kenneth G. Wynne Brown, Anchor House, LongcrossRoad, Chertsey; Keith Julyan Day, 19, Treemount Court, Grove Ave.,Epsom, both of Surrey, England [22] Filed: March 2, 1970 [21] Appl. No.:15,789

US. Cl. ..287/189.36 F, 287/ 126, 287/189.36 D Int. Cl ..F16b 5/00 Fieldof Search....287/189.36 C, 189.36 D,

[56] References Cited UNITED STATES PATENTS Moore ..287/ 109 UX Margis..285/328 X Vincent et a1. ..161/162 X Thassy ..151/37 UX' OTHERPUBLICATIONS Steel Construction Manual of the American Institute ofSteel Construction, 5th Edition, 3rd Printing, dated US. Patent OfficeLibrary on Aug. 27, 1947; page 314 cited, Library Identification: TA-684- A46- 1947.

Primary Examiner-David J. Williamowsky Assistant Examiner-Wayne L. SheddAtt0rney--Woodhams, Blanchard & Flynn [57] ABSTRACT The mating fayingsurfaces in a structural steel-work joint are protected by a layer ofcorrosion-resisting material such as primer or galvanizing. This layercarries a further layer of a friction agent comprising a binder andfriction-increasing particles such as grit or amorphous aluminumparticles.

Both layers can be works-applied for greater reliability andconsistency. The joint can be dismantled and reassembled withoutdifficulty. The layer of corrosive-resisting material will be applied asan a11-over protective layer for complete steel works components aftercleaning off mill-scale.

12 Claims, 4 Drawing Figures PATENTEDSEP 19 m2 EMZ m VE/V 729:5

y MIA 4M, flW Q m BOLTED-UP FRICTION JOINTS IN STRUCTURAL STEEL-WORKBACKGROUND OF THE INVENTION The present invention relates to bolted-upfriction joints in structural steel-work.

In such joints, shearing forces between two members are transmitted byfriction between faying surfaces of the two members, the two fayingsurfaces being tightly clamped together by high-strength friction-gripbolts.

An object of the present invention is to reduce the risk of slippagebetween faying surfaces in a bolted-up friction joint while at the sametime protecting the faying surfaces against corrosion. In conventionalpractice, red lead is often applied to mating surfaces before a joint isbolted-up but such use of red lead so reduces the co-efficient offriction between faying surfaces that it cannot be used in bolted-upfriction joints. The present British Standard Specification calls for nopaint on faying surfaces but rusting in the joint might ensue, therebyreducing its load carrying capacity and running the risk of looseningthe joint and/or the bolts and even of fracturing the bolts.

BRIEF DESCRIPTION OF THE INVENTION In accordance with the presentinvention a faying surface of a structural steel-work member is cleanedfree of mill scale and a layer of corrosion resisting material such aspaint or hot-dip galvanizing is applied to it. Then a friction agent, inthe form of a binder containing particles of friction-increasingparticulate material is applied to the said layerand allowed to dry andcure after which the faying surface maybe boltedup against the matingfaying surface of another structural member with high-strengthfriction-grip bolts.

In one form of embodiment, the particulate material is in the form ofparticles of hard grit or gritlike material of size and shape such thatwhen the joint is boltedup, at least some of the particles willpenetrate the corrosion-resisting layer on each surface and embedthemselves into the underlying metal so as to key the two fayingsurfaces together against the possibility of slip.

In another form of embodiment, in particulate material is amorphousaluminum or aluminum alloy particles of such particle size distributionas to increase materially the shear strength of a film applied to eachof the co-operating faying surfaces of the structural members which areultimately secured together with the same high-strength friction-gripbolts.

With all forms of embodiment, the steel-work members may be grit blastedand primed, or galvanized, in order to provide a corrosion-resistinglayer all over. The friction agent may then be applied to the fayingsurfaces and allowed to dry and cure, all these steps being convenientlycarried out under the better controlled and supervised conditions in thefactory or steelworks and away from the site. Thus no specialpreparation of the faying surfaces is required on site, therebyminimizing the amount of supervision required to ensure correctconstruction of the steel-work joints. Moreover, it is still possibleafter the steel-work has been erected on site to dismantle all or partof it, for example to permit the passage of some bulky object, withoutin any way affecting the properties of the fay- Ill 2 ing surfaces orprejudicing their performance after reassembly, an operation impossiblewith site-applied epoxy resin adhesives directly bonding two steel-workmembers together. I

In any of the forms of embodiment referred to above, the binder may becold-curing synthetic resin.

In the first kind of embodiment the grit or gritlike substance may be analumina-zirconia abrasive percent aluminum oxide, 20 percent zirconiumoxide) preferably within the size range of 50 to F.E.P.A. (Federation ofEuropean Producers of Abrasives). A high proportion of metallic zincdust may be included to give mechanical support to the grit and toprovide further resistance to corrosion.

Grit of approximately size 60 F.E.P.A. has shown particularly promisingresults with grit-blasted steel profiles in the range of 0.002 to 0.004in. peak-to-valley-height. Other examples of grit or gritlike materialswhich may be considered for appropriate cases are diamond particles,silicon carbide and tungsten carbide and hardened steel particles.

BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings, whichare given by way of example only,

FIG. 1 is a detail of a cross section through a faying surfacev of theinvention, on an enlarged scale,

FIG. 2 is a view similar to FIG. 1 but showing two faying surfacestightly clamped together,

FIG. 3 is an elevational view of a steel-work joint constructed as atest set, and

FIG. 4 is a section of the test set of FIG. 3, on the line 4-4.

In FIGS. 1 and 2, the reference 1 denotes the steel of steel-workmembers. The steel 1 carries a layer 2 of corrosion-resisting materialsuch as an etch primer which in turn carries a layer of friction agentcomprising grit particles 3 embedded in a binder 4.

In an example of the first embodiment, a suitable composition for thefriction agent has been found to be as follows:

Metallic Zinc Powder 75% (by weight) Other Pigments 1% AluminumZirconium Oxide Grit 4% Solvents 14% Epoxy Resin 6% Using such acomposition, the following test results were obtained:

Slip Loads in Ions Force The same witha Slip-factor is calculated fromthe following formula:

In examples of the second embodiment, suitable compositions have beenfound to be as follows:

Z-Pack Polyurethane Amorphous Aluminum Powder 70% (by weight) (grade100-200 British Standard mesh) Polyester Resin 7% Isocyanate Hardener.Solvents 18% l-Pack Polyurethane Amorphous Aluminum Powder 70% (byweight) Polyurethane Solution 25% Solvents 2% In order to obtain themaximum co-efficient of friction in the joint, the proportion ofaluminum should be as high as possible. However, to enable thecomposition to be applied like a paint, for example by brushing, it maybe found that it is not possible to increase the proportion of aluminummuch beyond the values given above.

Using such a composition the following test results were obtained usingthree sandwich test sets of the kind shown in FIGS. 3 and 4, undertension.

The test set shown comprises two steel tension plates 11 and 12 whichare connected together by two fishplate members asstraps l3 and 14. Theadjacent edges of the tension plate 11 and 12 are separated by a gap 15.The straps l3 and 14 are tightly clamped against the tension plates 13and 14 by high-strength bolts 16 and 14 are treated as described above.The readings X, 4 5 Y indicate the tensions at which the first andsecond joints slip yielded.

With Pre-fabrication The same, with further Primer (Zinc/Epoxy)Application of Aluminum Epoxy Friction Agent.

1X 25.2 34.5 It 25.2 34.5 2X 26.0 32.6 ZY 28.8 32.6 3X 24.8 33.2 3Y 27.731.0 Average: 26.28 33.07 Tension in bolts: 21 tons 21 tonsapproximately Average slip factor: .312 .394 Improvement due to frictionAgent: about 25% pressive load of 16 tons forboth tests.

By Torque Testing Torque By Slip Testing, Load in Tons at 14' radiusSlip Factor Set A .250 (avenge of 2) .370 Set 8 .255 .390 Set C .2505.380 Then .2518 tons of torque load is equivalent to .380

' slip factor.

or 0.1 ton of torque is equivalent to approximately .15 slip factor.

Using the same composition but with 60 F .E.P.A. grit added andmaintaining a compressive load of 16' tons for all tests, the followingresults were obtained and the slip factors calculated:

v Equivalent 1 Torque in tons slip factor Set No. 53 .378 .565 .365 .545.340 .510

Giving an average slip factor of .540.

Improvement due to friction agent: 42.2%.

With galvanizing, the following results were given:

Average torque Treatment load in tons Set No. G1 Nil .160 Set No. G3FEPA 60 Friction l 86 Agent. Set No. 65 FEPA Friction .240 Agent.

Improvement in friction of G5 over G1: 50%

Using 16 tons compressive load and testing by the torque method thefollowing results were obtained:

Equiva- Average improvement due to the friction agents:

With 2 pack Polyurethane With 1 pack Polyurethane We claim: 1. In abolted-up friction joint in structural steelwork, a rigid structuralsteel-work member having a substantially flat faying surface which iscleaned of mill scale, said faying surface having at least one bolt holetherethrough, and a high strength bolt extending through said bolt holeclamping said faying surface tightly against a further similar fayingsurface of a further rigid structural steel-workmember, comprising theimprovement wherein friction-increasing compositionmeans is applied tosaid faying surface for increasing the frictional characteristicsthereof, said frictionincreasing composition means being applied to saidfaying surface in surrounding relation to said bolt hole, saidfriction-increasing composition means including a hardenable syntheticbinder material forming a solid surface layer on said faying surface,said composition means also including friction-increasing material inparticulate form in said binder material, said frictionincreasingmaterial comprising hard grit-like particles capable of embeddingthemselves in the metal of the steel-work member, the layer offriction-increasing composition means on said faying surface beingpositioned to overlie said further faying surface, said gritlikeparticles being of a size and shape relative to the thickness of saidlayer of friction-increasing composition means such that when saidfaying surface is tightly compressed against said further faying surfaceof said further structural steel-work member at least some of saidparticles penetrate both faying surfaces and embed themselves in themetal of the structural steel-work members, the periphery of the regiondisposed between the faying surfaces in which is disposed said layer offriction-increasing composition means being open.

2. The combination according to claim 1, in which said grit-likeparticles is an abrasive within the size range of 50 to 120 F.E.P.A.

3. The combination according to claim 1, in which said grit-likeparticles is an alumina-zirconia abrasive.

4. The combination according to claim 1, in which said surface layeralso includes metallic zinc powder.

5. The combination according to claim 1, in which said particulatematerial is aluminum alloy particles.

6. The combination according to claim 5, in which said aluminum alloyparticles are substantially in the range of 100-200 British Standardmesh.

7. The combination according to claim 1 wherein the said binder is acold setting resin.

8. The combination according to claim 7, in which said resin is an epoxyresin.

9. The combination according to claim 7, in which said resin is apolyurethane.

10. The combination according to claim 9, in which said resin is aone-pack polyurethane binder.

11. The combination member according to claim 1, in which the fayingsurface is hot-dip galvanized prior to said composition means beingapplied thereto.

12. in a bolted-up friction joint in structural steelwork includingfirst and second structural steel-work members each having asubstantially flat faying surface which is cleaned of mill scale'andcarries a layer of corrosion-resisting material, said faying surfacesbeing disposed so as to face one another, each said faying surfacehaving at least one bolt hole therethrough, and a high strength boltextending through said bolt hole clamping said first and secondstructural steel-work members tightly together with said faying surfacesbeing disposed closely adjacent and directly opposite one another,comprising the improvement wherein friction-increasing composition meansis applied to each said faying surface for increasing the frictionalcharacteristics thereof, said friction-increasing composition meansincluding a binder material selected from the group consisting of epoxyresins and polyurethane resins, the binder material forming a solidsurface layer on said corrosion-resisting layer, said composition meansalso including friction-increasing material in particulate form in saidbinder material, said frictionincreasing material consisting of gritarticles having a high shear strength and hardness rela ve to saidfaying surfaces the layers of friction-increasing composition means onsaid faying surfaces being disposed in overlying engagement with oneanother when said first and second steel-work members are fixedlyinterconnected by said bolt, said grit particles being of a size andshape relative to the thickness of said layers of friction-increasingcomposition means such that when said faying surfaces are tightlycompressed against one another at least some of said particles penetrateboth layers of corrosion resisting material and embed themselves intothe underlying metal, the periphery of the region disposed between thefaying surfaces in which is disposed said overlying layers offriction-increasing composition means being open.

2. The combination according to claim 1, in which said grit-likeparticles is an abrasive within the size range of 50 to 120 F.E.P.A. 3.The combination according to claim 1, in which said grit-like particlesis an alumina-zirconia abrasive.
 4. The combination according to claim1, in which said surface layer also includes metallic zinc powder. 5.The combination according to claim 1, in which said particulate materialis aluminum alloy particles.
 6. The combination according to claim 5, inwhich said aluminum alloy particles are substantially in the range of100- 200 British Standard mesh.
 7. The combination according to claim 1wherein the said binder is a cold setting resin.
 8. The combinationaccording to claim 7, in which said resin is an epoxy resin.
 9. Thecombination according to claim 7, in which said resin is a polyurethane.10. The combination according to claim 9, in which said resin is aone-pack polyurethane binder.
 11. The combination member according toclaim 1, in which the faying surface is hot-dip galvanized prior to saidcomposition means being applied thereto.
 12. In a bolted-up frictionjoint in structural steel-work including first and second structuralsteel-wOrk members each having a substantially flat faying surface whichis cleaned of mill scale and carries a layer of corrosion-resistingmaterial, said faying surfaces being disposed so as to face one another,each said faying surface having at least one bolt hole therethrough, anda high strength bolt extending through said bolt hole clamping saidfirst and second structural steel-work members tightly together withsaid faying surfaces being disposed closely adjacent and directlyopposite one another, comprising the improvement whereinfriction-increasing composition means is applied to each said fayingsurface for increasing the frictional characteristics thereof, saidfriction-increasing composition means including a binder materialselected from the group consisting of epoxy resins and polyurethaneresins, the binder material forming a solid surface layer on saidcorrosion-resisting layer, said composition means also includingfriction-increasing material in particulate form in said bindermaterial, said friction-increasing material consisting of grit particleshaving a high shear strength and hardness relative to said fayingsurfaces the layers of friction-increasing composition means on saidfaying surfaces being disposed in overlying engagement with one anotherwhen said first and second steel-work members are fixedly interconnectedby said bolt, said grit particles being of a size and shape relative tothe thickness of said layers of friction-increasing composition meanssuch that when said faying surfaces are tightly compressed against oneanother at least some of said particles penetrate both layers ofcorrosion resisting material and embed themselves into the underlyingmetal, the periphery of the region disposed between the faying surfacesin which is disposed said overlying layers of friction-increasingcomposition means being open.